diff options
| -rw-r--r-- | kernel/smp.c | 83 |
1 files changed, 44 insertions, 39 deletions
diff --git a/kernel/smp.c b/kernel/smp.c index bbedbb7..6ecf4b9 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -74,9 +74,16 @@ static void generic_exec_single(int cpu, struct call_single_data *data) spin_unlock_irqrestore(&dst->lock, flags); /* - * Make the list addition visible before sending the ipi. + * The list addition should be visible before sending the IPI + * handler locks the list to pull the entry off it because of + * normal cache coherency rules implied by spinlocks. + * + * If IPIs can go out of order to the cache coherency protocol + * in an architecture, sufficient synchronisation should be added + * to arch code to make it appear to obey cache coherency WRT + * locking and barrier primitives. Generic code isn't really equipped + * to do the right thing... */ - smp_mb(); if (ipi) arch_send_call_function_single_ipi(cpu); @@ -104,6 +111,14 @@ void generic_smp_call_function_interrupt(void) int cpu = get_cpu(); /* + * Ensure entry is visible on call_function_queue after we have + * entered the IPI. See comment in smp_call_function_many. + * If we don't have this, then we may miss an entry on the list + * and never get another IPI to process it. + */ + smp_mb(); + + /* * It's ok to use list_for_each_rcu() here even though we may delete * 'pos', since list_del_rcu() doesn't clear ->next */ @@ -154,49 +169,37 @@ void generic_smp_call_function_single_interrupt(void) { struct call_single_queue *q = &__get_cpu_var(call_single_queue); LIST_HEAD(list); + unsigned int data_flags; - /* - * Need to see other stores to list head for checking whether - * list is empty without holding q->lock - */ - smp_read_barrier_depends(); - while (!list_empty(&q->list)) { - unsigned int data_flags; - - spin_lock(&q->lock); - list_replace_init(&q->list, &list); - spin_unlock(&q->lock); + spin_lock(&q->lock); + list_replace_init(&q->list, &list); + spin_unlock(&q->lock); - while (!list_empty(&list)) { - struct call_single_data *data; + while (!list_empty(&list)) { + struct call_single_data *data; - data = list_entry(list.next, struct call_single_data, - list); - list_del(&data->list); + data = list_entry(list.next, struct call_single_data, + list); + list_del(&data->list); - /* - * 'data' can be invalid after this call if - * flags == 0 (when called through - * generic_exec_single(), so save them away before - * making the call. - */ - data_flags = data->flags; - - data->func(data->info); - - if (data_flags & CSD_FLAG_WAIT) { - smp_wmb(); - data->flags &= ~CSD_FLAG_WAIT; - } else if (data_flags & CSD_FLAG_LOCK) { - smp_wmb(); - data->flags &= ~CSD_FLAG_LOCK; - } else if (data_flags & CSD_FLAG_ALLOC) - kfree(data); - } /* - * See comment on outer loop + * 'data' can be invalid after this call if + * flags == 0 (when called through + * generic_exec_single(), so save them away before + * making the call. */ - smp_read_barrier_depends(); + data_flags = data->flags; + + data->func(data->info); + + if (data_flags & CSD_FLAG_WAIT) { + smp_wmb(); + data->flags &= ~CSD_FLAG_WAIT; + } else if (data_flags & CSD_FLAG_LOCK) { + smp_wmb(); + data->flags &= ~CSD_FLAG_LOCK; + } else if (data_flags & CSD_FLAG_ALLOC) + kfree(data); } } @@ -375,6 +378,8 @@ void smp_call_function_many(const struct cpumask *mask, /* * Make the list addition visible before sending the ipi. + * (IPIs must obey or appear to obey normal Linux cache coherency + * rules -- see comment in generic_exec_single). */ smp_mb(); |
